WASHINGTON -- Rep. Rick Berg (R-N.D.), who is running for the state's open U.S. Senate seat, was caught off guard when approached by a voter who wanted to know the state's minimum wage.

In the exchange, posted by the North Dakota Democratic Party, a young woman approaches Berg at a campaign event and asks him what the minimum wage is in the state.

"Hmmm," Berg replies. He then points to someone standing nearby and says, "This guy would know."

"I think it's probably seven something," he adds. "It depends -- they don’t have a minimum wage for waitresses in North Dakota."

They then ask someone else. That person says it's the same as the federal minimum wage, and asks Berg, "You know what that is?"

"Oh! Put it back on my shoulders!" the congressman jokingly replies.

The minimum wage in North Dakota is $7.25 an hour, which is the same as the federal minimum wage.

Senate candidates are increasingly being tripped up on minimum wage questions. At a recent Missouri GOP Senate debate, the four candidates vying for a chance to challenge Sen. Claire McCaskill (D-Mo.) did not know the amount of the minimum wage. They opposed raising it, however.

Berg voted against raising the minimum wage while in the state legislature in 1999, 2005 and 2007. In 2003, he also voted against a bill that would have required government contractors to pay a living wage.

When considering a proposal to raise the state minimum wage from $4.75 to $5.15 an hour in January 1997, the Bismark Tribune reported that Berg responded, "You would say that government should control that choice rather than the employer?"

He has, however, voted repeatedly to increase the salary of state lawmakers. Berg was the 14th richest member of the U.S. House in 2010, according to the Center for Responsive Politics, a nonpartisan group that tracks money in politics.

Berg is expected to face off against Democrat Heidi Heitkamp in the November election. The race will likely be tight, and Republicans and Democrats are spending on ads.

"It's fair to say that Rick Berg has spent too much time in Washington if he can't name the minimum wage," said Brandon Lorenz, spokesman for Heitkamp's campaign. "But that's no surprise from someone with a history of looking out for millionaires like himself, by voting for the Ryan budget that cuts taxes for the wealthy and raises Medicare premiums."